From: Sridhar Seshasayee Date: Mon, 5 Jun 2023 08:11:28 +0000 (+0530) Subject: PendingReleaseNotes: Document mClock scheduler fixes and enhancements X-Git-Tag: v19.0.0~1061^2 X-Git-Url: http://git.apps.os.sepia.ceph.com/?a=commitdiff_plain;h=49aad118aa41a8e66ab65f229c5633ee18c6a3b2;p=ceph.git PendingReleaseNotes: Document mClock scheduler fixes and enhancements Signed-off-by: Sridhar Seshasayee --- diff --git a/PendingReleaseNotes b/PendingReleaseNotes index a5a20b9dbe62f..e9df0a071e6f3 100644 --- a/PendingReleaseNotes +++ b/PendingReleaseNotes @@ -139,6 +139,29 @@ * CEPHFS: After recovering a Ceph File System post following the disaster recovery procedure, the recovered files under `lost+found` directory can now be deleted. * core: cache-tiering is now deprecated. +* mClock Scheduler: The mClock scheduler (default scheduler in Quincy) has + undergone significant usability and design improvements to address the slow + backfill issue. Some important changes are: + * The 'balanced' profile is set as the default mClock profile because it + represents a compromise between prioritizing client IO or recovery IO. Users + can then choose either the 'high_client_ops' profile to prioritize client IO + or the 'high_recovery_ops' profile to prioritize recovery IO. + * QoS parameters like reservation and limit are now specified in terms of a + fraction (range: 0.0 to 1.0) of the OSD's IOPS capacity. + * The cost parameters (osd_mclock_cost_per_io_usec_* and + osd_mclock_cost_per_byte_usec_*) have been removed. The cost of an operation + is now determined using the random IOPS and maximum sequential bandwidth + capability of the OSD's underlying device. + * Degraded object recovery is given higher priority when compared to misplaced + object recovery because degraded objects present a data safety issue not + present with objects that are merely misplaced. Therefore, backfilling + operations with the 'balanced' and 'high_client_ops' mClock profiles may + progress slower than what was seen with the 'WeightedPriorityQueue' (WPQ) + scheduler. + * The QoS allocations in all the mClock profiles are optimized based on the above + fixes and enhancements. + * For more detailed information see: + https://docs.ceph.com/en/latest/rados/configuration/mclock-config-ref/ >=17.2.1